Fleischer had the idea of using frames of a live action film as the basis for drawing animation, his patent for the rotoscope[?] was granted in 1917, although Max and Dave Fleischer made their first cartoon using the device in 1915.

In 1919 he established Fleischer Studios for producing animated cartoons and short subjects. His brothers Dave Fleischer and Richard Fleischer also worked there.

Fleischer invented the rotograph, the first technique for adding animated characters to live backgrounds. Extensive use of this technique was made in Fleischer's Out of the Inkwell series, one of the highlights being a boxing match between the cartoon Koko the Clown and a live kitten.

Fleischer was also responsible for the "follow the bouncing ball" sing along cartoons.